1. Field of the Invention
The present invention relates to a quality control method and a quality control system on a production line for fabricating products including a series of lots such as semiconductor products and, more particularly, to quality control method and system on a production line that collect data by measurements or inspections of fabricating products derived by an arbitrary manufacturing process or manufacturing equipment and monitor the quality characteristics of fabricating products associated with the results of the processing to thereby prevent troubles with quality.
2. Description of the Related Art
A semiconductor production line is made up of processing steps such as formation of films and photoengraving and inspection steps such as inspection of film thicknesses and inspection of development. To stabilize the quality and to improve the productivity, it is essential to establish a method of managing the quality of fabricated products. In recent years, a quality control method using a database and providing concentrated management of products has generally been established. In particular, the database is created by collecting various kinds of data including data about actual results (such as lot names, process step names, product types, and date of completion), data obtained by actual measurements or inspections of the characteristics of lots undergone processing performed by an arbitrary process step or manufacturing apparatus, statistical data obtained by statistically processing the aforementioned kinds of data, data about the equipment (such as process conditions and maintenance), and data about electric power and energies (such as blackout, stoppage of water supply, and power supplied to an air conditioner). In this prior art method, data obtained by actual measurements or inspections of individual lots are monitored such that the average values of the measured data do not exceed preset threshold values. If any one of the average values exceeds the threshold value, it is determined that an abnormality has taken place, and an alarm is issued. The associated section of the plant will search for the cause and take measures.
A specific example of method of judging an abnormality is proposed, for example, in Japanese Patent laid-open No. Hei. 9-50949 using a computer for monitoring production and quality in a production management and computational system. This computer employs three decision patterns A, B, and C as shown in FIG. 4. In this figure, CV indicates the centerline of data used as a reference for control. Lines LU and LL indicate an upper threshold value and a lower threshold value, respectively. Values obtained by actual measurements such as average values of actual measurements are indicated by small black circles P. The pattern A of FIG. 4(a) indicates a case in which actually obtained values P, such as some average values of actual measurements, are higher than the upper threshold LU of the data used as a reference for quality control and other average values P are lower than the lower threshold LL thereof The pattern B of FIG. 4(b) indicates a case in which successively obtained actual values P are all at one side of the center value CV of the data used as a reference for quality control. The pattern C of FIG. 4(c) indicates a case in which actually obtained values P are all at an angle in succession to the center value CV of the data used as a reference for quality control. These cases are judged to be abnormal. FIG. 5 shows the transition of the average value of measured dimensions. This transition is judged to be abnormal from the pattern C described above.
In the prior art quality control method described above, statistical data consisting of average values of measurements has been mainly monitored to judge whether the quality characteristics of fabricated products are abnormal. If the average value of measurements goes over the upper threshold value for the control or goes under the lower threshold value, the lot has often already become defective. Therefore, it has been difficult to prevent troubles with quality or equipment. Furthermore, if quality trouble due to a cause that is difficult to find takes place, the equipment or lot is stopped for a long time. This deteriorates productivity. In addition, as proposed in the above-cited Japanese Patent laid-open No. Hei. 9-50949, in order to grasp a phenomenon in which average values of measured dimensions are at an angle in succession, the average values of measurements of plural lots are necessary (8 lots in the case of FIG. 5). This delays taking measures against the trouble. As a result, many defective lots are produced, increasing the damage.
The present invention has been made to solve the foregoing problems.
It is an object of the present invention to provide a quality control method of preventing troubles with quality by detecting the trendency or fluctuations of quality characteristics of products fabricated on a production in early stage.
It is another object of the invention to provide a quality control system that implements the quality control method described in the immediately preceding paragraph.
According to the present invention, a quality control method on a production line including at least one fabricating step for fabricating products including a series of lots, said quality control method comprising:
a inspection step for inspecting the fabricating products associated with results of the fabrication step of line;
a storing step for storing data obtained by the inspection step to a memory; and
a management step for managing the variations of the data to manage the quality characteristics of the fabricating products by using the data stored in the memory;
wherein in the management step, the trend in quality is managed by using absolute values of differences between same kinds of the data obtained at given measurement points regarding each of the fabricating products.
In one feature of the quality control method on the production line, wherein in the management step, the trend in quality is managed by using absolute values of differences between maximum and minimum values of same kinds of the data obtained at given measurement points regarding each lot of the fabricating products.
In another feature of the quality control method on the production line, wherein in the management step, the trend in quality is managed by using absolute values of differences between same kinds of the data obtained at given measurement points regarding each of the fabricating products, based on a threshold value and wherein if any one of the absolute values of differences exceeds the threshold value, an alarm is issued.
According to the invention, another quality control method on a production line including at least one fabricating step for fabricating products including plural groups of a series of lots, said quality control method comprising:
a inspection step for inspecting the fabricating products associated with results of the fabrication step;
a storing step for storing data obtained by the inspection step to a memory;
a processing step for statistically processing the data stored in the memory to thereby derive statistical data; and
a management step for managing the variations of the statistical data to manage the quality characteristics of the fabricating products;
wherein in the management step, the trend in quality is managed by using absolute values of differences between same items of the statistical data derived from the two groups of the series of lots processed by the fabricating step in succession.
In a still feature, the quality control method on the production line, wherein in the management, the trend in quality is managed by using the values of differences between average values derived from the two groups of the series of lots processed by the fabricating step in succession.
In a another feature, the quality control method on the production line, wherein in the management step, the trend in quality is managed by using absolute values of differences between same items of the statistical data derived from the two groups of the series of lots processed by the fabricating step in succession, based on a threshold value and wherein if any one of the values of differences exceeds the threshold value, an alarm is issued.
In the quality control method for a production line for fabricating products in accordance with the present invention, a trend in quality of the series of products is managed, using either absolute values of differences between same kinds of the data obtained at given measurement points regarding each of fabricating products, or absolute values of differences between same items of the statistical data derived from the two groups of the series of lots processed by the fabricating step in succession. Consequently, troubles with quality can be prevented. Hence, the quality of the products can be stabilized. Also, the productivity can be enhanced.
According to the invention, a quality control system on a production line including plural fabricating steps for fabricating products including a series of lots, said quality control system comprising:
a quality characteristic data registration-and-processing means for storing data about actual results obtained by inspecting the fabricating products processed by the fabricating steps to a memory, said results including lot name of the products, process step name, product type, and date of processing;
a management condition registration-and-processing means registered with a method of judging whether each lot is defective and with an upper threshold value, a lower threshold value, and a processing method effected when an abnormality takes place;
a quality characteristic abnormality decision means for receiving data about results of inspections on the fabricating products from quality characteristic data registration-and-processing means, and judging the data obtained by the inspections based on the abnormality decision method registered in the management condition registration-and-processing means; and
a notice-and-display means for giving a notice of results of a decision made by the quality characteristic abnormality decision means and displaying the results;
wherein said quality characteristic abnormality decision means acting to manage a trend in quality of said fabricating products, using absolute values of differences between same kinds of the data obtained at given measurement points regarding each of the lots.
Also, according to the invention, a quality control system on a production line including plural fabricating steps for fabricating products including plural groups of a series of lots, said quality control system comprising:
a quality characteristic data registration-and-processing means for storing data about results and data obtained by inspecting the fabricating products processed by the fabricating steps to a memory and for statistically processing the date to obtain statistical data, said results including lot name of the products, process step name, product type, and date of processing;
a management condition registration-and-processing means registered with a method of judging whether each lot is defective and with an upper threshold value, a lower threshold value, and a processing method effected when an abnormality takes place;
a quality characteristic abnormality decision means for receiving data about the results of inspections on the fabricating products and said statistical data from said quality characteristic data registration-and-processing means, and judging the statistical data by the abnormality decision method registered in said management condition registration-and-processing means; and
a notice-and-display means for giving a notice of results of a decision made by the quality characteristic abnormality decision means and displaying the results;
wherein said quality characteristic abnormality decision means acting to manage a trend in quality of said groups of series of lot, using absolute values of differences between the same items of said statistical data derived from the two groups of the series of lots processed by same fabricating step in succession.
In the quality control system for a production line for fabricating products in accordance with the present invention, a trend in quality of the series of products is managed, using either absolute values of differences between same kinds of the data obtained at given measurement points regarding each of fabricating products, or absolute values of differences between same items of the statistical data derived from the two groups of the series of lots processed by the fabricating step in succession. Therefore, troubles with quality can be prevented. In consequence, the quality of the products can be stabilized. Also, the productivity can be improved.
Other objects and features of the invention will appear in the course of the description thereof, which follows.